A popular and effective way of fishing involves dragging a fishing line from the back of a boat at a slow, constant velocity. This technique is referred to as trolling. Often, the motor that is used on a boat is not capable of running constantly at a low enough speed to maintain the desired slow trolling velocity. Over the years, people have used a type of device referred to as a "trolling plate" to limit boat speed. A trolling plate typically employs a rigid plate suspended behind the propeller of the motor. The plate deflects a significant amount of the water stream generated by the propeller, thereby limiting the velocity of the boat.
A problem with trolling plates that has been worked on for many years is that sometimes the operator of the boat forgets that the plate is down. The operator then causes the propeller to accelerate without releasing the trolling plate. Consequently, the trolling plate may be bent or damaged. Some people have tried to design automatic release mechanisms for trolling plates. For example, U.S. Pat. No. 5,711,241 to Dyer uses a release mechanism that includes a pair of adjustably biased rollers on opposing sides of the plate for contacting notches in trolling plate ears. A significant problem with the Dyer trolling plate is that sometimes one side of the plate releases before the other side releases, causing the plate to twist and possibly break. U.S. Pat. No. 3,136,280 discloses a trolling plate that pivots to the horizontal position in response to water pressure above a certain threshold. One problem with the plate described in the '280 patent is that the spring force used to maintain the trolling position of the plate is difficult to tune or adjust for the particular motor or trolling application.
It is an object of the invention to provide a trolling plate that releases reliably when water pressure generated by a motorized propeller exceeds a predetermined threshold. Another object of the invention is for a trolling plate to be adjustable such that the release threshold can be altered to suit the particular motor and boat specifications.